Weaken. The correct answer choice is (D)
Because frequent VDT users suffered from headaches more often than other office workers did, the researchers concluded that VDTs caused the headaches. As with most arguments of this type, a positive correlation between two variables is interpreted to suggest the presence of a causal relationship between them:
- Cause Effect
VDT → Headache
Since we are asked to weaken a causal argument based on the findings of a survey, our job will typically involve showing either that (1) an alternate cause is responsible for the stated effect, or (2) that the data upon which the survey was based is erroneous. In this particular case, maybe excessive VDT use and headache are both the result of a third, unrelated cause, such as working overtime. Alternatively, maybe frequent headaches make people overestimate how much time they spent using VDT, which would undermine the data used to make the causal statement.
Answer choice (A): Even if few office workers participated in regular health programs, it is still entirely possible that VDT caused their headaches. The frequency with which the workers participated in such programs would only impact the likelihood that their headaches would be diagnosed and treated, not their occurrence in general.
Answer choice (B): The severity of the headaches experienced does not undermine the conclusion that they are all caused by VDT. This answer choice is incorrect.
Answer choice (C): At first, this seems like an attractive answer because some students might interpret "eyestrain" as an alternate cause for the workers' headaches. However, since eyestrain was itself caused by VDTs, this answer choice only explains how VDTs cause headaches and thus strengthens the researchers' argument.
Answer choice (D): This is the correct answer choice. If the workers who experienced frequent headaches tend to overestimate how much time they spent using VDTs, then the survey was based on potentially erroneous data, which undermines the validity of the causal claim.
Answer choice (E): The fact that stress is not correlated with the use of VDT does not establish that headaches are not either. Because the analogy assumes a correlation between two conditions that may have nothing in common, this answer choice does not weaken the argument and is incorrect.